Abstract. The AMAXDOAS instrument is an airborne multi-axis DOAS instrument
covering the spectral range from 300 to 600 nm. During one
flight of the SCIAVALUE campaign on 19 March 2003, the AMAXDOAS
onboard the DLR Falcon detected tropospheric NO2 over
Europe under both cloudy and cloud free conditions. By combining
the measurements in nadir and zenith direction, and analysing the
spectra in the UV and the visible spectral region, information was
derived on where the bulk of the observed NO2 was located.
Vertical columns of up to 5.7x1016 molec cm-2 were observed close to Frankfurt, with a
distribution peaking in the boundary layer and in good agreement
with surface measurements. On several occasions, strong
tropospheric NO2 signals were also detected when flying
above clouds. The ratio of zenith and nadir measurements indicates
that the NO2 observed was located within the cloud, and
assuming the same profile as for the cloud free situation the
NO2 vertical column was estimated to be 5.0x1016 molec cm-2. The results are relevant for the
retrieval of tropospheric NO2 columns from space-borne
instruments in cloudy situations.